Janakkala (Finnish pronunciation: [ˈjɑnɑkːɑlɑ]) is a municipality of Finland. Its administrative centre is in Turenki. Janakkala is located along Highway 3 (E12) in the province of Southern Finland and is part of the Kanta-Häme region. To the south, Janakkala shares a boundary with Riihimäki, the northern neighbour being Hämeenlinna. It is 16 kilometres (9.9 mi) from Turenki to Hämeenlinna, 94 kilometres (58 mi) to Tampere, and 96 kilometres (60 mi) to Helsinki.

The municipality has a population of 15,995 (30 June 2025) and covers an area of 586.07 square kilometres (226.28 sq mi) of which 38.63 km² (14.92 sq mi) is water. The population density is 29.22 inhabitants per square kilometre (75.7/sq mi). In Janakkala the rate of unemployment is 9.7% and the rate of municipal taxes is %.^[when?] The municipality is unilingually Finnish.

The history of Janakkala stretches far back to prehistoric times, as evidenced by numerous archaeological finds and traces of settlement. The area has been inhabited at least since the Stone Age, and especially the Vanajavesi valley and the Laurinmäki region have served as centers of human habitation for thousands of years. Several significant Iron Age burial sites and sacrificial stones have been found in Janakkala, including a Viking Age cremation cemetery discovered in 2016. The area also features hillforts, with the most famous being Hakoinen, which once served as an important place of refuge and a center of trade.

Christianity gradually arrived in the Janakkala region from the start of the 9th century, although its official establishment took longer. Before the breakthrough of Christianity, Janakkala was part of the larger Greater Vanaja region, but it became a parish around the year 1300. The first written mention of Janakkala dates back to 1341, when Bo Jonsson issued a judgment in Janakkala.

The Swedish era, beginning in the 13th century, marked a period when Janakkala became an important base for Swedish administration in Häme (Tavastia). The region's versatile waterways provided excellent conditions for trade and agriculture, and Hakoisten hillfort protected the settlement and its connections to other areas. The role of the church and administration grew significantly over time.

Janakkala is renowned as a manor parish: it is home to many well-known manors, such as Hakoinen, Harviala, Hyvikkälä, and Vanantaa. For a long time, influential noble families resided in these manors, and manor life has left a lasting impact on the local culture and landscape.

Industrialization began early in Janakkala compared to many other rural municipalities. The Tervakoski paper mill was established as early as 1818, growing into a significant locality. Leppäkoski, in turn, developed a strong identity through its brick industry, while the significance of the Turenki locality increased thanks to sugar and ice cream factories. The reform of municipal administration, which developed Finnish society, resulted in Janakkala becoming its own municipality under the 1865 decree.

Janakkala's identity includes a strong connection to history and culture, which is still visible in its settlements, museums, and monuments: the Laurinmäki tenant farmer museum, old manors, Hakoisten linna and church, and many other historical sites all tell the story of a parish with a diverse and long history, from the Stone Age to the present day.